1. Field of the Invention
This invention relates generally to the preparation of nucleophilically ring-substituted aromatic compounds, and more specifically to the preparation of such aromatic compounds by the reaction of aromatic-thallium (III) metallates with a source of the nucleophilic substituent.
2. Description of the Prior Art
It is known that aromatic compounds undergo metallation when reacted with a thallium (III) salt, resulting in the formation of an unsaturated organometallic compound (hereinafter referred to as "aromatic-thallium (III) metallate") through replacement of a carbon-hydrogen bond by a carbon-thallium (III) bond. An example of such a metallation reaction, the thallation of benzene, may be illustrated by the following equation (1): ##STR1## wherein X is an organic radical, such as for example CH.sub.3, CH(CH.sub.3).sub.2 or CF.sub.3.
These metallates have been employed to obtain such aromatic derivatives as (1) aryl iodides by reaction with aqueous potassium iodide (E. C. Taylor et al., 92(7) J. Amer. Chem. Soc. 2176 (1970) ("Taylor I"); A. McKillop et al., Tetrehedron Letters, 2427 (1969) ("McKillop I"); E. C. Taylor et al. 3 Accts. Chem. Res. 338 (1970) ("Taylor II"); E. C. Taylor et al., 93 (19) J. Amer. Chem. Soc. 4841 (1971) (Taylor III"); E. C. Taylor et al, 93 (19) J. Amer. Chem. Soc. 4845 (1971) ("Taylor IV")); (2) aryl nitrates by reaction with NO.sub.2 (Davies, et al., J. Chem. Soc. Perkins I, 65 (1975)); (3) nitro aryl iodides by successive reactions with acetyl nitrate and iodine (E. C. Taylor et al., 40 J. Org. Chem. 3441 (1975)); and (4) nitro aryls by reaction of dichlorothallium (III) aryl metallate with nitrosyl chloride (E. C. Taylor et al., 38 J. Org. Chem. 2088 (1973)).
Also, aromatic-thallium (III) metallates have been used in the preparation of aryl alcohols by reaction of the metallate with lead tetraacetate, followed by addition of triphenyl phosphine to the reaction mixture and hydrolysis of the resulting intermediate with aqueous base. (Taylor II supra at pages 344-345; and E. C. Taylor et al., 92(11) J. Amer. Chem. Soc. 3520 (1970) ("Taylor V")). Deuterated aryls have also been formed by reaction of the metallate with lithium aluminum deuteride or by reduction with aluminum amalgam in D.sub.2 O (Taylor et al. II supra at page 345 and M. J. Zelesko, Ph. D. Thesis, Princeton University (1970)).
Bisaryl thallium compounds (which are formed by refluxing aromatic-thallium (III) metallate in acetone followed by addition of water to the reaction mixture) have also been treated by similar methods to obtain aryl iodides and aryl alcohols. Thus, such bisaryl thallium compounds have been reacted with excess I.sub.2 in CHCl.sub.3 to form iodides and with lead tetraacetate/triphenyl phosphine/aqueous base to form aryl alcohols. See E. C. Taylor et al. 40 (16) J. Org. Chem. 2351 (1975) ("Taylor VI").
However, a broader application of metallates in the synthesis of substituted aromatic compounds has been heretofore believed to require photolysis to initiate a free radical reaction involving Ar radicals, in which "Ar" represents the aryl moiety. Thus, aryl thiocyanates and aryl cyanides have been formed by reaction of an aromatic-thallium (III) metallate with KSCN and KCN, respectively, with photolysis required of the reaction mixture to form the desired substituted aromatic compound. (See E. C. Taylor et al, Synthesis 38 (1971) as to the aryl thiocyanates and Taylor II supra and Taylor V, supra as to the aryl cyanides). Likewise, aryl thiophenols have been formed by stepwise reaction of an aromatic-thallium (III) metallate with ##STR2## and water, followed by photolysis of the resulting intermediate (Taylor II, supra at pages 343-344), and aniline has been reportedly formed by photolysis of phenyl ditrifluoroacetato thallium in the presence of ammonia (Taylor II, supra at page 344). Finally, bisaryls (such as biphenyl) have been formed from the bisaryl thallium compounds of Taylor VI, supra, by photolysis of the latter thallium compounds in the presence of benzene.* FNT *See also E. C. Taylor, et al., 92 (20) J. Amer. Chem. Soc. 6088 (1970)-bisaryls via photolysis of arylthallium ditrifluoroacetates in benzene.
While it has been suggested to use the reaction of aryl thallium dicarboxylates and nitrosyl chloride (in which aryl nitroso compounds are formed) to introduce amino functionalities into aromatic nuclei (See, e.g., A. McKillop and E. C. Taylor, Advances in Organometallic Chemistry, vol. 11, 147, 170-171 (1973) ("McKillop II")), such reactions are not readily adaptable to direct amination of aromatic-thallium (III) metallates, and conversion of aryl nitroso compounds to the corresponding aryl amines requires increased processing time and equipment.